Probing Proton Spin Structure: A Measurement of g₂ at Four-momentum Transfer of 2 to 6 GeV²

Abstract

The Spin Asymmetries of the Nucleon Experiment investigated the spin structure of the proton via inclusive electron scattering at the Continuous Electron Beam Accelerator Facility at Jefferson Laboratory in Newport News, VA. A double-polarization measurement of polarized asymmetries was performed using the University of Virginia solid polarized ammonia target with target polarization aligned longitudinal and near transverse to the electron beam, allowing the extraction of the spin asymmetries A 1 and A 2 , and spin structure functions g 1 and g 2 . Polarized electrons of energies of 4.7 and 5.9 GeV were scattered to be viewed by a novel, non-magnetic array of detectors observing a four-momentum transfer range of 2 to 6 GeV 2 . This document addresses the extraction of the spin asymmetries and spin structure functions, with a focus on spin structure function g 2 , which we have measured as a function of x and W in four Q 2 bins.

The extraction of the spin structure function, g2 (and g1) at low Bjorken x

“…• The open geometry of the UVa solid polarized target, that allows for flexible relative orientations of the beam helicity and the target spins, coupled with the high proton polarizations [16]. …”

“…In addition, the pairs of electrons are detected in coincidence around this angle. In all, nine Møller data measurements were done periodically during the SANE experiment [16]. Due to the fact that during an experimental run, the beam polarization is not The jumps in Figure 3.4 are due to the fact that the longitudinal polarized beam was simultaneously delivered to two experimental halls of the three experimental halls (A, B and C).…”

“…The slow raster is operated in a 2 cm maximum diameter spiral pattern. Generally, the raster system is used to spread the beam over the polarized target's surface area uniformly to avoid rapid depolarization due to heating and radiation damage [16]. can be found in [18].…”

“…The microwaves needed to drive the polarization enhancement in DNP were supplied by an Extend Interaction Oscillator (EIO) [16]. The EIO was located above the target during the experiment, coupled to either target material cups by a switching junction and over-sized CuNi wave-guides broadcast microwaves evenly over the cups.…”

“…Thus, the material has to be replaced as soon as the depolarization rate is high enough to cause the time cost of more frequent anneals to be greater than the time cost of uninstalling the insert from the fridge, swapping in new materials and reinstalling the insert. More details on radiation damage and annealing can be found in [16] and [53].…”